The present invention relates to an actuator and in particular, but not exclusively, to a jam-tolerant electromechanical actuator for moving an aircraft component.
Actuators may be used to cause movement of aircraft components such as the landing gear of an aircraft. An actuator system for extending the landing gear of an aircraft should of course be of high integrity and should have a very low risk of failure. For example, it is important for there to be provided a secondary, or emergency, extension system for extending the landing gear from the up-locked position (before landing) and for opening the landing-gear bay doors, in the event of a loss of the normal extension system. Such an emergency extension system should be required not only to extend the landing gear from its up-locked position, but also from any intermediate position in the event of a failure of the gear to retract fully for example.
A landing gear extension system of the prior art, using a hydro-mechanical actuator, comprises both a normal extension system, which relies on active operation of the hydro-mechanical actuator, and an emergency extension system. The emergency extension system, also known as a free-fall system, operates by allowing the gears to extend and the doors to open under gravity. During use of the emergency extension system, the hydraulic fluid dynamics within the hydro-mechanical actuator provides sufficient damping during extension (towards gear down-lock position) to preserve the gear from damage. The configuration of the hydro-mechanical actuator, when the landing gear has reached its fully deployed position, is such that the actuator does not react any load resulting from landing gear or airframe flexure (given that the piston of the hydraulic actuator is not otherwise prevented from sliding inside the cylinder of the actuator).
There is a desire to reduce the reliance on hydraulic systems in large commercial aircraft and thus there is currently a desire to use electric actuators, where previously hydro-mechanical actuators were used. There are two types of electric actuators that might be used, namely, an indirect drive actuator or a direct drive actuator. Indirect drive actuators use gear boxes, worm screws or similar mechanisms to convert the rotating motion of an electric motor into either low-speed/high-thrust linear motion or low speed/high torque rotary motion, whereas direct drive actuators (also known as linear motors) directly convert electricity into linear motion.
Direct drive actuators are highly reliable, but may not be capable of meeting the extension/retraction requirements of certain applications in an aircraft. Indirect drive actuators are capable of meeting many of the requirements (such as mass, volume occupied, power output, and extensions achievable), but are more likely to jam than direct drive actuators or hydraulic cylinders as a result of the mechanisms used to convert motion of the motor to the actuating motion required.
The present invention seeks to provide an actuator that mitigates one or more of the above-mentioned disadvantages. Alternatively or additionally, the present invention seeks to provide an improved actuator. Alternatively or additionally, the present invention seeks to provide a jam-tolerant actuator for use on an aircraft, that does not need to rely on a central hydraulic system of the aircraft, the actuator for example being in the form of an electric indirect drive actuator.